Volcano Ground-Warping Could Predict Ash Plume Height

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The way a volcano warps the ground might predict how high an
eruption's ash plume will get, which in turn might help
scientists gauge the impact the explosion could have before it
happens, researchers say in a new study.

Scientists analyzed Grímsvötn for the study,, a volcano near the
middle of the Vatnajökull ice cap on the volcanically active
island of Iceland.

"Grímsvötn volcano is Iceland's most frequently erupting volcano," said
study lead author Sigrún Hreinsdóttir, a geophysicist at the
University of Iceland in Reykjavik.

Grímsvötn's 2011 eruption was its greatest since 1873, erupting
about 9.5 billion cubic feet (270 million cubic meters) of
material. The resulting
ash plume reached 15.5 miles (25 kilometers) high, closing
air traffic over northern Europe and causing the cancellation of
about 900 passenger flights.

The researchers monitored how the volcano deformed the ground
using high-precision GPS
sensors and tilt-meters, devices that measure changes in
their own position and tilt over time. They compared this data
with the height of the eruption plume over time, using radar data
and photographs taken during the eruption.

"I am interested in better understanding volcanic
activity using GPS and one key aspect is to improve eruption
forecasting," Hreinsdóttir said. "We started monitoring the
volcano with GPS measurements in 1992."

The investigators discovered the height of the ash plume varied
in tandem with the GPS readings. These findings suggest both were
controlled by changes in pressure within the volcano's magma
chamber, which sits at a depth of about 1 mile (1.7 kilometers) .

Intriguingly, the ground began to warp an hour or so before the
plume erupted. This suggests that GPS data could be used to
predict the eruption and evolution of an ash cloud before it
happens, providing timely warnings, the researchers say.

"Could we perhaps in the future be able to give out short-term
forecasts of an imminent eruption and be able to say something
about how big the eruption was going to be?" Hreinsdóttir told
LiveScience's OurAmazingPlanet. "GPS is becoming more and more
common in a volcanic setting for monitoring unrest, possibly
giving us information on the plume height."

The next step is "to investigate available deformation signals
from significant eruptions at other volcanoes," Hreinsdóttir
added.

Hreinsdóttir and her colleagues detailed their findings online
today (Jan. 12) in the journal Nature Geoscience.